I have a 2000 Sony CD / FM / duel Cassette deck stereo that I'd like to hook up to a 2007 speaker system that I had hooked up to my old desktop PC. I thought maybe it would be as easy as plugging in the red/white cords, but not so.
Sony Model hcd-mc3av
2.1 channel multimedia active speaker system
From Sony' "Audio Out" (RCA second row from the top) to that no-name "Input" (RCA second row from the top) should work. But - your CD changer already has amplifiers, and I doubt they are worse than this CO21.
If it still does not work, it's time to see where the signal gets lost. Get a RCA-to-3.5mm cable, and try the CO21 with your phone.